Communications devices, such as mobile telephones or personal computers, allow a subscriber to attach to a communication network and communicate with other devices. Furthermore, a growth area is that of machine to machine (M2M) communication, in which communications are sent between different devices without human intervention. Examples of the use of M2M communication include the provision of sensor networks (for example, networks for monitoring weather conditions,), surveillance equipment (for example alarm systems, video monitoring, and so on), vehicle fleet management, vending machines, monitoring manufacturing and so on.
It is predicted that in the long term future, there will be billions of M2M devices, and the number of M2M devices will far exceed the number of devices used for communication between humans (such as mobile telephones, personal computers and so on).
When a device wishes to attach to an existing 3GPP mobile access network, it must register with the network and be authenticated. Registration and authentication are handled using information contained in a Subscriber Identity Module (SIM) or Universal Subscriber Identity Module (USIM) at the device. Each device is uniquely identified by an International Mobile Subscriber Identity (IMSI) that is stored at the SIM/USIM. The IMSI is a number range managed by ITU-T, where the number is split into three sections as follows:
1. Mobile Country Code (MCC) that uniquely identifies the country (three digits).
2. Mobile Network Code (MNC) that identifies the home Public Land Mobile Network (PLMN) of the mobile subscriber (two or three digits).
3. Mobile Subscriber Identification Number (MSIN) that identifies the mobile subscriber within a PLMN (nine to ten digits).
By way of example, if the MCC is 429, the MNC is 01, and the MSIN is 1234567890, then the IMSI is 429011234567890.
If the predictions for the growth in communication devices such as M2M devices are accurate, then some countries will face a shortage of IMSI numbers. An obvious solution to a potential shortage of IMSI numbers is to extend the length of the IMSI, for example by making the MSIN twelve digits long. However, this is not a practical solution as it would require changes to terminals, access network procedures and all network nodes.
If the prediction of billions of devices holds, some countries will start to have a shortage of IMSI numbers. An obvious solution to this would simply be to extend the IMSI length. However, this would make it difficult in existing systems as it would require changes to existing mobile terminals and all other network nodes, as well as changes to access network procedures.